A warning to those using hand pumps

[PCPhack]

I wish that I had taken more before pictures, but I didn't. I have been refurbishing an old Flex, that was used for about 2 years with a hand pump. As I have suspected all along about hand pumps without proper moisture filtering, they set up a perfect scenario for parts corrosion inside of airguns. Here is a picture of the original Flex valve that I am fixing back up for another gentleman, since I put a new JSAR valve in the Flex. This original valve would not seal any more due to corrosion in the oring groove. I repolished the valve end and groove. I have it pressurized now to make sure it will hold air. The remnant black area here is where the worst of it was. There was even some light pitting inside the groove. So add good moisture filters to your hand pumps, and pack areas like this in your guns with lots of silicone grease to displace any potential water.

[RDB]

And yet, one member just tore down a disco after ten years of hand pumping and not any rust to speak of. Im sure a lot has to do with the area one lives at and shorter pumping sessions where less heat is generated. Cant argue that a filter is money well spent though.

[PCPhack]

Rod, I recall reading that thread. Indeed, it would seem that it all depends on your location during all those pumping sessions.

[Wayne52]

Here in Michigan it has never bothered my Prod at all, a hand pump is what I use to fill pistols when out hunting on the state land.

[Ribbonstone]

Here is the question:

Did the corrosion start behind the o-ring and creep along the surface forward (which would not be the fill devices fault)...or start in front of the o-ring and creep it's way backwards (which would be moisture in the air tube).

And can your really swear it wouldn't have happened with a tank or compressor?

[PCPhack]

Well those are all good questions, and ones that I can't answer, except that there was at least a little of similar signs inside the air reservoir at the bottle block. Here is the kicker though, when I received the gun it was depressurized, so there could have been creep from the outside in. There is really no way to know. The only conclusion is to be dilligent to avoid moisture however you can.

[dv8eod]

The materials used in the construction can't be discounted, either.

[PCPhack]

The Flex has a steel tube, so this is an area with steel and aluminum against each other.

[anti-squirrel]

materials, local humidity, and quality of assembly (IE: were those O-rings properly lubed with a hydrophobic grease) are the Big 3; no different than the HPA systems on board a submarine.  Keep the air dry coming in and- as long as the internals had no moisture and were properly lubed- you'll have no problems.

The big enemy is oxidation.  I won't deny a moisture trap or dessicant filtration would be a great addition, though.

The good news is pitting and corrosion can be addressed the same way you would on multi-million-dollar valves in the Navy: epoxy + machining (even if doing things by hand).  Once the points of oxidation are clean and dry, dress with epoxy, refinish, and apply O-rings and dive grease (or similar) and keep on pumping/shooting.

[Ribbonstone]

Reguardless of how it got there...you've got the air tube fully open and the valve out. Fix the o-ring seal. Now just buff in a thin coating of real silicon grease (like you were waxing a car) inside the tube and put it back together.

[PCPhack]

Yes, it is fixed and pressurized in a spare Marauder tube I have right now. I want to be sure it doesn't leak before giving the valve to the person I promised it to.

[Nomadic Pirate]

I think dessicants on handpumps are way overrated,

In over a decade handpumping my PCPs I found zero signs of moisture in the tubes.

[DHunter]

I think dessicants on handpumps are way overrated.

In over a decade handpumping my PCPs I found zero signs of moisture in the tubes.

And you're in humid Hawaii, right?

[Nomadic Pirate]

Yes and never lived in an air conditioned house.

[robertr]

I have experienced moisture in my pump but never in the rifle.

[Nomadic Pirate]

I have experienced moisture in my pump but never in the rifle.

Absolutely, everytime I would open up my pumps I would find a lot of moisture on the tube, and the HILLs ad just as much if not more moisture then others.

[Doug Wall]

I think dessicants on handpumps are way overrated,

In over a decade handpumping my PCPs I found zero signs of moisture in the tubes.

I know that  you have mentioned that before, but there may be some circumstances that lead to more corrosion. In talking to someone who repairs (factory trained) Crosman guns, a few things come up, but probably shouldn't be generalized to all guns.
1) Almost all of the leaking guns that he works on have been hand pumped.
2) 3000 psi fill guns show more corrosion than 2000 psi fill guns.

There are also some differences between pumps, in the way that they vent moisture. Some pumps have the vent even with the pump outlet, and some pumps have the vent below the pump outlet (better moisture trapping?)

The warm climate in Hawaii might also be a difference. In colder climates, condensation might be more of an issue.

[porkchopexpr3ss]

even if you lived in 1% percent humidity, you would be at 100% with moisture condensing out when compressed to our pressures.

[AlanMcD]

People keep thinking the temperature and relative humidity of the source air has a lot to do with how dry the air is coming out of the hand pump - the reality is that it has nothing to do with that at all!  This is because the air coming out of the pump (once pressurized) will have a relative humidity of essentially 100% (meaning that it is saturated with as much water vapor as it can hold at that pressure and temperature), and all the remaining water vapor in the charge air will have condensed out into liquid water.

The critical factor is not the air going in, but how hot the pump gets, because the hotter the pump, the hotter the air charge, and thus the more water vapor will be in the air and transferred into the gun - to condense out as liquid water as it cools further.  The key is pump slowly (so the air charge has a moment to cool in the base of the pump after each stroke), and in short sessions (so the pump can cool down, allowing the next set of strokes to have the water vapor condense out too).  As Manny has shown, if done right there is no problem - if you find water condensed in guns that are filled by hand pumping, the person doing the pumping was going too fast and taking too many strokes in each session.

The only thing the relative humidity of the source air has to do with it is the amount of water that condenses out during the pumping session . . . . and driers on the air going in help, but they don't eliminate the need to use the proper technique.

[robertr]

 As long as you have a good desiccant filter on the intake of the pump you should be ok. I can fill either the Marauder up to 3000psi from 2000psi or my Scorpion SE to 3250psi from 2000psi all in one session, no breaks, takes just over 2 minutes. A few minutes for a break in between if I fill both rifles one after the other.